1. Field of the Invention
The present invention relates to a composition for removing a photoresist residue and a polymer residue remaining after dry etching and after ashing.
2. Description of the Related Art
In recent years, to miniaturize semiconductor circuit elements and to increase the performance of them, new wiring materials and interlayer insulating film materials have been employed. For example, copper and an alloy having copper as a main component (hereinafter, called a ‘copper alloy’) have been used as new wiring materials for the purpose of reducing wiring resistance and inter-wiring capacitance. Copper wiring is formed by, for example, a damascene process in which, after copper is embedded using sputtering or electro-plating in a trench formed as a wiring pattern in an interlayer insulating film, an unwanted copper film portion is removed using chemical mechanical polishing (CMP), etc. Similarly, with regard to the copper alloy, there are examples in which it is used for wiring by a process analogous to the damascene process.
The introduction, as a new interlayer insulating film material, of an organic film represented by an aryl ether compound, a siloxane film represented by HSQ (Hydrogen Silsesquioxane) and MSQ (Methyl Silsesquioxane), and a porous silica film, which are low permittivity (low-k) materials, is also being investigated.
It is however clear that the above-mentioned copper, copper alloy, and various types of low permittivity films have low chemical resistance compared with aluminum, aluminum alloy, and silicon oxide film, which are conventional materials. Moreover, since the various types of low permittivity films, which are new materials, have a chemical composition different from the silicon oxide film, which is a conventional material, a process for fabricating a semiconductor device is carried out under conditions that are different from conventional ones.
In a process for fabricating a semiconductor device dry etching, in which an interlayer insulating film or a wiring material film formed on a substrate is subjected to patterning using a photoresist pattern as a mask, has conventionally been carried out. As a posttreatment for dry etching, after the resist pattern is ashed and removed by an ashing treatment, a photoresist residue, a polymer residue, etc. partially remaining on the treated surface is usually removed by a special purpose composition (remover liquid). The photoresist residue referred to here means an incompletely ashed organic compound such as a photoresist or an anti-reflection film remaining on the substrate surface after dry etching and ashing, and the polymer residue referred to here means a fluorocarbon deposit originating from an etching gas during dry etching that remains on an etched material wall surface as a by-product, a side wall polymer such as a compound between a wiring metal and an etching gas (also called a side wall protecting film or a rabbit ear), and an organometallic polymer and a metal oxide remaining on a side face and a base face of a via hole.
When the interlayer insulating film employs the above-mentioned organic low permittivity film represented by an aryl ether compound, with regard to an etching gas for patterning of the interlayer insulating film, a mixed gas of nitrogen and hydrogen or a mixed gas of nitrogen and helium is generally used. Since during etching these etching gases simultaneously etch a photoresist formed from an organic compound in the same manner as for the organic low permittivity film, an inorganic material (silicon oxide, silicon nitride, etc.) for which the etching gas has a lower selectivity than for the above-mentioned organic low permittivity film may be used as a mask.
When the interlayer insulating film is a siloxane film, represented by MSQ, which is easily altered by ashing, since in the same manner as for the above-mentioned case of the organic low permittivity film a photoresist formed from an organic compound is etched, an inorganic material for which an etching gas has a lower selectivity than for the low permittivity film formed from the siloxane film may be used instead as the mask in dry etching.
In this way, when the interlayer insulating film formed from a low permittivity film is dry etched using as a mask an inorganic material whose selectivity is lower than that of the low permittivity film, an inorganic mask layer formed on the interlayer insulating film is firstly dry etched using a photoresist mask, the photoresist is ashed and removed by ashing, and an inorganic mask pattern is thus obtained. Furthermore, this inorganic mask is used for dry etching of the interlayer insulating film.
After dry etching the interlayer insulating film using the above-mentioned production step, it is mainly a polymer residue that remains on the surface of the substrate, and no photoresist residue, which is an incompletely ashed substance of an organic compound such as a photoresist or an anti-reflection film, remains.
On the other hand, when multilayer wiring is formed, after plasma TEOS covering a lower layer metal wiring pattern is formed, a low permittivity layer covering inter-wiring gaps and the wiring pattern is formed so as to reduce inter-wiring capacitance, on top of this layer a cap layer is then formed by means of plasma TEOS, and after planarization by CMP is carried out, a via hole for a tungsten plug is formed by a photolithographic process using a photoresist (ref. JP, A, 2000-306999). In this case, since a photoresist residue remains on the surface and a polymer residue remains within the via hole, it is necessary to remove them. This demands a composition that is not corrosive toward silicon oxide formed by the plasma TEOS.
In a process for fabricating a semiconductor device using a new material such as copper, a copper alloy, or various types of low permittivity film, there is the new problem that the conventional photoresist residue removal composition cannot be employed. For example, a representative conventional photoresist residue removal composition containing an alkanolamine and a quaternary ammonium compound used for removing a photoresist residue formed on a substrate having aluminum, an aluminum alloy, or a silicon oxide film corrodes copper and copper alloy, which have low corrosion resistance and, furthermore, causes etching and structural change in various types of low-k film.
Hence, as a new type of residue removal composition for removing a photoresist residue and a polymer residue formed on a substrate having copper, a copper alloy, or a low-k film, the following five types have been reported.
1) A composition containing an alkanolamine, a nitrogen-containing compound as a corrosion inhibitor, and water. Examples of the alkanolamine include N-methylaminoethanol and monoethanolamine, and examples of the corrosion inhibitor include uric acid, adenine, caffeine, and purine (ref. JP, A, 2002-99101).
2) A composition containing an aliphatic polycarboxylic acid, a reducing material such as glyoxylic acid, and water. Examples of the aliphatic polycarboxylic acid include oxalic acid, malonic acid, tartaric acid, malic acid, succinic acid, and citric acid, and examples of the reducing material include glyoxylic acid, ascorbic acid, glucose, and mannose (ref. JP, A, 2003-167360).
3) A composition containing one type or two or more types of fluorine compound, one type or two or more types of glyoxylic acid, etc. and water. The fluorine compound is ammonium fluoride, and examples of the glyoxylic acid, etc. include glyoxylic acid, ascorbic acid, glucose, fructose, lactose, and mannose (ref. JP, A, 2003-280219).
4) A composition containing a fluorine compound such as ammonium fluoride, a water-soluble organic solvent, a buffer agent, water, and a basic compound. Examples of the basic compound include aqueous ammonia, alcoholamines, hydroxylamines, polyalkylene polyamines, piperazines, and morpholines (ref. JP, A, 2003-241400).
5) A composition containing a salt of hydrofluoric acid and a base containing no metal, a water-soluble organic solvent, an organic acid, an inorganic acid, and water. Examples of the organic acid include formic acid, acetic acid, oxalic acid, tartaric acid, and citric acid (ref. JP, A, 2004-94203).
However, the above-mentioned compositions 1) to 5) have the following problems.
With regard to the composition 1), the amount of alkanolamine makes up 40 to 90 mass % of the composition, and the burden on the environment is large.
With regard to the composition 2), it is disclosed in JP, A, 2000-167360 that a photoresist residue can be removed by immersion at 25° C. for 10 minutes. However, when the composition is used in a single wafer washing system, which has been used frequently in recent years and requires a short processing time, its removal performance is not always sufficient.
With regard to the composition 3), as shown in a comparative example of the present application, the etching rate for an altered layer on an MSQ surface formed during dry etching and ashing of a low permittivity film formed from a siloxane film such as MSQ is extremely high. Because of this, when this composition is used, there is a possibility that the actual etching dimensions might be larger than the intended etching dimensions. Furthermore, since this composition has no component that dissolves an organic component, a photoresist residue or a polymer residue containing a large amount of organic component, etc. might not be removed adequately. Moreover, when this composition is recycled within a washing system, after a large number of wafers are treated the content of the components in the composition changes because of concentration due to evaporation of water, consumption of the components by the treatment, dilution by contamination of a rinsing liquid, etc., and target characteristics cannot be obtained.
With regard to the composition 4), since an organic solvent and a basic compound are contained therein, the composition can dissolve an organic component; since a buffer agent is contained therein, consideration has been given to the characteristics not changing accompanying a change in the content of the components when the composition is recycled, but as with the composition 1) the amount of organic solvent makes up 50 mass % or more of the composition, and the burden on liquid waste treatment is very heavy.
With regard to the composition 5), since an organic solvent is contained therein, the composition can dissolve an organic component, but as with the composition 4) the amount of organic solvent makes up 50 mass % or more of the composition, and the burden on liquid waste treatment is very heavy.